No Limit Trailing Arm Rear Suspension

[robnolimit]

Way back in the late '90's, we made a coil over mount set up for these trucks that mounted the shock behind the axle. - Just like what everyone else is doing now. It's all about leverage, so the farther back you are from the trailing arm pivot, the less the shock is leveraged. A shock/spring behind the axle is great for hauling rocks, but looses it's ability to help the tire stay stuck to the road when the truck is empty (no rocks). While our coil-over may seam 'out of place' compared to others, think about the location of the factory coil spring, not too far from our new mounting points. As to shock valving/action, it's just a question of matching the valving to the ratios and weights. Just like the difference of front shocks and rear shocks, 50% leveraged compared to 1-1 ratio. Also, many suspension designs incorporate the shock angle as it relates to the suspension travel angle, which is usually no straight up and down, as the suspension travels in arcs, and the shock needs to stay close to 90 degrees to the suspension motion, not 90 degrees to the ground.
Thanks for the input, and all of those things are a factor we need to think about.

[crakarjax]

Originally Posted by robnolimit

A shock/spring behind the axle is great for hauling rocks, but looses it's ability to help the tire stay stuck to the road when the truck is empty (no rocks).

Can you explain why this is?

I'm imagining two shock locations, one in front and one behind the axle and both mounted to the frame rails. Both locations are selected for identical shock angle and length. I'm considering the frame to be actually stiff between the two shock mounting points. The only difference that I can think of here is the force applied to the shock due to leverage, which can be compensated for with different valving.

[robnolimit]

Originally Posted by crakarjax

Can you explain why this is?

I'm imagining two shock locations, one in front and one behind the axle and both mounted to the frame rails. Both locations are selected for identical shock angle and length. I'm considering the frame to be actually stiff between the two shock mounting points. The only difference that I can think of here is the force applied to the shock due to leverage, which can be compensated for with different valving.

well, yes and no. Yes, it's leverage and force, it's also shaft speed of the shock. And, while it is reasonably true that custom valving and spring rates can be fitted to be a perfect match, the question is, are they available? Look at the current crop of aftermarket coil-over. Do they spec 'front' or 'rear' valve codes? Remember that most 'front' shocks are at close to 2 to 1 leverage ratio, and most 'rear' shocks are at a 1 to 1 ratio, or close. Factor in the weights and it is clear that the typical front shock need 4x the valving resistance as compared to a rear shock (very wide liberal estimate for discussion) While they do offer adjustable valving, it is all in a set range. So , our job is to use what is available, test it on a shock dyno, set the valving range and then design a way to use off the shelf parts and make them work to the best of their ability.

[crakarjax]

Originally Posted by robnolimit

well, yes and no. Yes, it's leverage and force, it's also shaft speed of the shock. And, while it is reasonably true that custom valving and spring rates can be fitted to be a perfect match, the question is, are they available? Look at the current crop of aftermarket coil-over. Do they spec 'front' or 'rear' valve codes? Remember that most 'front' shocks are at close to 2 to 1 leverage ratio, and most 'rear' shocks are at a 1 to 1 ratio, or close. Factor in the weights and it is clear that the typical front shock need 4x the valving resistance as compared to a rear shock (very wide liberal estimate for discussion) While they do offer adjustable valving, it is all in a set range. So , our job is to use what is available, test it on a shock dyno, set the valving range and then design a way to use off the shelf parts and make them work to the best of their ability.

From what I read just now, shock leverage ratio is the ratio of wheel movement to shock shaft movement -- I might be misunderstanding though, because the only way to get a 1:1 ratio would be to have a shock mounted along the axis of axle motion, correct?